This invention relates to utilizing alkane, e.g., methane, as a fundamental component for the production of oxygenates, especially alkanol and dialkylether, e.g., methanol and/or dimethylether. More particularly, the invention relates to a unique conversion scheme using electrophile ions, e.g., chloronium and/or nitrosonium ions to produce the oxygenates.
Natural gas is an abundant fossil fuel resource. Recent estimates place worldwide natural gas reserves at about 35xc3x971014 standard cubic feet, corresponding to the energy equivalent of about 637 billion barrels of oil.
A major source of methane is natural gas. Primary sources for natural gas are the porous reservoirs generally associated with crude oil reserves. From these sources come most of the natural gas used for heating purposes. Quantities of natural gas are also known to be present in coal deposits and are by-products of crude oil refinery processes and bacterial decomposition of organic matter. Natural gas obtained from these sources is generally utilized as a fuel at the site.
The composition of natural gas at the wellhead varies but the major hydrocarbon present is methane. For example, the methane content of natural gas may vary within the range of from about 40 vol. % to 95 vol. %. Other constituents of natural gas may include ethane, propane, butanes, pentane (and heavier hydrocarbons), hydrogen sulfide, carbon dioxide, helium and nitrogen.
Natural gas is classified as dry or wet depending upon the amount of condensable hydrocarbons contained in it. Condensable hydrocarbons generally comprise C3+ hydrocarbons although some ethane may be included. Gas conditioning is required to alter the composition of wellhead gas, processing facilities usually being located in or near the production fields. Conventional processing of wellhead natural gas yields processed natural gas containing at least a major amount of methane.
A significant portion of the known natural gas reserves is associated with fields found in remote, difficultly accessible regions. Many of these distant sources are not amenable to transport by pipeline. For example, sources that are located in areas requiring economically unfeasible pipeline networks or in areas requiring transport across large bodies of water are not amenable to transport by pipeline. This problem has been addressed in several ways. One such solution has been to build a production facility at the site of the natural gas deposit to manufacture one specific product. This approach is limited as the natural gas can be used only for one product, preempting other feasible uses. Another approach has been to liquefy the natural gas and transport the liquid natural gas in specially designed tanker ships. Natural gas can be reduced to {fraction (1/600)}th of the volume occupied in the gaseous state by such processing, and with proper procedures, safely stored or transported. These processes, which involve liquefying natural gas at a temperature of about xe2x88x92162 xc2x0 C., transporting the gas, and revaporizing it, are complex and energy intensive.
Still another approach has been the conversion of natural gas to higher order hydrocarbons that can be easily handled and transported. The term xe2x80x9chigher order hydrocarbonxe2x80x9d refers to a hydrocarbon having at least two carbon atoms. In this way easily transportable commodities may be derived directly from natural gas at the wellhead. The conversion of natural gas to higher order hydrocarbons, especially ethane and ethylene, retains the material""s versatility for use as precursor materials in chemical processing. Known processes are available for the further conversion of ethane and ethylene to other useful materials.
U.S. Pat. No. 4,199,533 discloses a process for converting methane to higher molecular weight hydrocarbons by using chlorine gas as a recyclable catalyst. The process produces ethylene as a major product along with hydrogen chloride, which is converted to chlorine for recycle in the system. Major drawbacks of the xe2x80x2533 process are the large amount of chlorine required, the necessity of regenerating chlorine from hydrogen chloride to maintain an economically viable system, and the need to use operating temperatures in excess of 1000xc2x0 C. to produce ethylene. Additionally, the required chlorine is corrosive under such operating conditions.
It is known to use chloronium ion in treating hydrocarbon conversion catalysts. For example, U.S. Pat. No. 3,950,270 to Paynter et al. discloses iridium-containing reforming catalysts containing iron or bismuth wherein agglomerated iridium is readily dispersible by combining iron and bismuth with halide, e.g., chlorine, to provide a chloronium ion which reacts with iridium oxide, IrO2, to form IrO2Cl, which is more readily redispersed.
Another process for converting natural gas involves formation of methanol. For offshore and other difficult gas producing locations, it is preferable to provide a process which is simple to operate. Because methanol production from natural gas is the simplest way to convert gas to liquid, it is highly desirable for on-site use. U.S. Pat. No. 3,898,057 to Moller et al. discloses a process for converting natural gas to a mixture of carbon monoxide and hydrogen at the site of production, converting the mixture to methanol, and transporting the methanol to a place of consumption where it is burnt or reconverted into methane. However, more efficient ways of converting methane to methanol would be highly desirable.
The electrophilic activation of methane in the presence of metal complexes such as (bipyridinium)PtCl2 has been disclosed. xe2x80x9cPlatinum Catalysts for the High-Yield Oxidation of Methane to a Methanol Derivativexe2x80x9d, Roy A. Periana, Douglas J. Taube, Scott Gamble, Henry Taube, Takashi Satoh, and Hiroshi Fujii, Science Apr. 24, 1998; 280: 560-564. However, the reaction rate in such systems is low, the regenerability and stability of the metal complexes is questionable, and it has not been proven that these reactions are truly catalytic and not stoichiometric in the metal complex. In contrast, a method which utilizes non-metal electrophiles would be desirable, particularly if such electrophiles were readily regenerable.
The present invention provides a method for converting alkanes, e.g., methane, to oxygenates, e.g., alkanols and/or dialkylethers. This method comprises electrophilicly activating alkane using electrophilic ions, e.g., halonium, such as chloronium, in combination with nitrosonium and/or nitronium, and substituting the activated methane with sulfate to provide a sulfate ester intermediate which is hydrolyzed to alkanol and/or dialkylether.
The present invention provides a method for converting alkane to oxygenate. The method comprises the following steps: (i) contacting an alkane-containing gas with non-metal, regenerable, electrophile ions in a concentrated sulfuric acid medium under conditions sufficient to provide electrophilicly activated alkane and reduced electrophile ions; (ii) contacting said electrophilicly activated alkane with sulfate to form a sulfate ester; (iii) exposing said sulfate ester to hydrolyzing conditions sufficient to convert it to oxygenate; and (iv) collecting said oxygenate.